Fluid cooling employing plural cold producing machines



G. PRAST Sept. 10, 1968 FLUID COOLING EMPLOYING PLURAL COLD PRODUCING MACHINES Filed Feb. 28, 1967 I5 Sheets-Sheet 1 i i H INVENTOR.

GIJSBERT PRAST AGENT Sept. 10, 1968 v cs. PRAST 3,400,544

FLUID COOLING EMPLOYING PLURAL COLD PRODUCING MACHINES Filed Feb. 28, 1967 3 Sheets-Sheet 2 INVENTOR. GIJSBERT PRAST gwwe.

AGENT 3 Sheets-Sheet 5 INVENTOR. susaam PRAST AGENT G. PRAST 5 2 r i N 5- :Iilili,

FLUID COOLING EMPLOYING PLURAL COLD PRODUCING MACHINES J 14 111G J q n\ V 7 2 2 3 2 2 2 Q Q Q H 0- 3 I 5 4 a 5 f 7 E 5 5 5 8 5 LC Sept. 10, 1968 Filed Feb.

Unitcdst tcs Pate t ABSTRACT OF THE DISCLOSURE A cooling device for a fluid comprising at l east two cold producing machines, each machine having at least one compression space and at least two expansion spaces of successively lower temperature with means communieating with said spaces, said means including at least one regeneratorQThe'fluid to be cooled passes through a duct system and is cooled in the expansion space of higher temperature in one machineand is further cooled in the like expansion space of the other machine, and thereafter being cooled in each further group of corresponding expansion spaces of lower temperature in each machine.

The invention relates to a device for cooling or condensing a medium, comprising at least one" machine for producing'cold, said machine having one or more compression spaces of variable volume, in which, in operation,

a higher average temperature prevails and which co-' operate with at least two expansion spaces also efvariable volume, in which, inoperation, sequentiallylower temperatures prevail, said spaces communicating with each other and each communication including at least. one

regenerator, through which a working medium can flow to and fro, said device comprising furthermore a, duct system through which a medium to be cooled or condensed can flow and whichis in-thermal contact in sequence with the Working medium in said expansion spaces of sequentially lower temperatures.

A device of the kind set forth is knownqln this device the cold producing machine is formed by a cold-gas refrigerator of the multi-space type, that isto say. a coldgas refrigerator comprising a plurality of, expansion spaces having a gradually lower temperature according as their distance from the compression space increases. In this device a medium can be cooled by establishing a thermal contact in a duct system between this medium and the expansion spaces of gradually lower temperatures. The medium is cooled to about the temperature, of theexpansion space of lowest temperature, the medium being so to say pre-cooled by vthe-thermal contact with the medium in the other expansion spaces of higher average temperatures. 4

The cooled medium, for'example helium, may then be expanded, so that it becomes liquid.

The final temperature ofthe medium to'be cooled is a fixed value, which is determined by the nature of the medium, its pressure and the intended use of the medium. I

Consequently, the temperature of the last expansion space and hence also that of the other expansion spaces are fixed. The quantity of cold produced in the various expansion spaces is, in general, higher according as the temperature in said spaces is higher.

This means that by means of a given machine only a given quantity of a medium can be cooled to the desired temperature. If a larger quantity of this medium has to be cooled to said temperature, it is, of course, possible to use two cold-gas refrigerators, in which part of the medium is in thermal contact with one machine and a further part with the other machine, so that the cold production and hence the quantity of medium that can be cooled are twice as high. When the number of machines is increased, the cold production and hence the quantity of medium to be cooled will rise directly proportionally to said number.

The'invention is based on the surprising effect that when using a plurality of cold producing machines a suitable choice of the order of succession in which the flow of medium to be cooled is brought into thermal contact with the various expansion spaces permits of attaining an increase in cold production (quantity of medium to be cooled) which is more than directly proportional to the number of machines employed.

For this purpose the device according to the invention is characterized in that it comprises at least two cold producing machines, in which the duct system is first in thermal contact with the expansion space of the highest temperature of the first machine, after which it is brought into thermal contact in order of succession with the corresponding expansion spaces of each of the further machines, the duct system being subsequently in thermal contact in the same order of succession with each further group of corresponding expansion spaces.

In this device the fiow of medium is passed along all expansion spaces.

It has been found that in this way a device comprising two cold producing machines is surprisingly capable of providing a cold production (quantity of cooled medium), which is about four times the production of one machine.

The invention will be described more fully with 'reference to the drawing.

FIG. 1 shows diagrammatically a device comprising two cold-gas refrigerators, which precool the gas to be FIG. 2 shows diagrammatically a device corresponding with that of FIG. 1, but it comprises three cold-gas ,with a driving gear (not shown), which is capable .of

moving said bodies with phase difference. During this movement the upper surface of the piston 1 various the volume of a compression space 6. The annular surface 7, formed by the transition between the displacer portions 2 and 3, acts upon the volume of an intermediate expansion space 8 and the upper face of the displacer por tion 3 varies the volume of a final expansion space 9. The compression space 6 communicates through a cooler 10,

I a first regenerator 11, a first freezer 12 with the intermediate expansion space 8. The intermediate expansion space 8 communicates through a second regeneator 13 and a second freezer 14 with the expansion space 9'. In operation very low temperatures can be attained in the expansion spaces 8 and 9, the temperature in the space 8 being higher than that in the space 9.

The device comprises furthermore a compressor 20 for compressing a medium of low condensation temperature, for example, helium. The outlet of compressed medium from said compressor communicates with a duct 21 for the high-pressure medium. This duct includes a great number of heat exchangers 22, in which the high pressure medium exchanges heat with the low pressure medium in the duct 23, joining the inlet of the compressor. The duct 21 includes furthermore heat exchangers 24, 25, 26 and 27, in which the high-pressure medium is consecutively in thermal contact with the expansion spaces 8 and 9 respectively of the cooling machine A.

In these heat exchangers the medium will be cooled to a gradually lower temperature. After the passage through the various heat exchangers the cooled medium is fed to a choking cock 29, in which the pressure of the medium is reduced. The liquefied medium is collected in a container 30, in which a cooling helix is arranged, through which a further medium can be passed. The vapour from the container 30 is fed back through the duct 23 to the inlet of the compressor 20.

It has been found that by causing the high-pressure medium to be in thermal contact in the given order of succession with the sequential expansion spaces of the two cold-gas refrigerators a quantity of medium can be cooled to the desired temperature which is about four times the quantity that can be cooled by one cold-gas refrigerator of similar structure.

Although in the device according to the invention the medium is allowed to expand in a choking cock 29, an ejector may be used for this purpose.

FIG. 2 shows a device in which the high-pressure medium is cooled by means of three cold-gas refrigerators A, B and C, each being of the type comprising three expansion spaces. The duct 21 is brought into thermal contact first with the expansion space 31 of the highest expansion temperature of each of the machines. Subsequently, the medium is in thermal contact in order of succession with the expansion spaces 8 and 9 of each of these machines. For the sake of clarity the heat exchangers in which the high-pressure medium exchanges heat with the low pressure medium returning through the duct 23 to the compressor are omitted.

Also in this device the quantity of medium that can be cooled to a given temperature will be considerably greater than three times the quantity that can be furnished by one machine.

FIG. 3 shows a device in which two cold-producing machines E and F of different structure are employed. Each of these machines comprises mainly a piston-like body of two portions 41 and 42 of difierent diameters, adapted to reciprocate in a cylinder. The piston-like body is linked by a piston rod 43 to a driving gear (not shown). During the movement the volumes of the spaces 44, 45 and 46 are varied.

The space 44 communicates through a cooler 47, a first regenerator 48 and a freezer 49 with the space 45, which, in turn, communicates by way of a second regenerator 50 and a second freezer 51 with the expansion space 46. In operation the space 44 is substantially at room temperature, whereas lower temperatures are attained gradually in the spaces 45 and 46.

The space 44 is provided with a duct 52, which communicates through a controllable closing member 54 and a container 55 with the outlet of the compressor 56. The space 44 is furthermore provided with duct 53, which communicates through a controllable closing member 57 and a container 58 with the inlet of the compressor 56.

This machine operates as follows. When the pistonlike body 41, 42 occupies its uppermost position, the controllable closing member 54 is opened and the spaces 44, 45 and 46 are filled with high-pressure medium. In the open position of the closing member 54 the piston-like body moves downwards. At a given instant the closing mernber 54 is closed and the closing member 57 opened;

the pressure in the spaces 44, 45 and 46 then drops, so that cold is produced in the spaces 45 and 46, which then contains the major portion of the medium.

This cold may be employed, in the same manner as in the device of FIG. 1, for cooling the high-pressure medium from a compressor 20. The system containing this highpressure medium is quite identical to that of FIG. 1, so that a further description may be dispensed with.

Also in this device the cold production will be more than proportional to that obtainable by one cold producing device.

It will be apparent from the foregoing that the invention provides a device for cooling a medium in which by a suitable choice of the order in which the medium is passed along the various cold places a surprising increase in the quantity of medium to be cooled can be achieved.

What is claimed is:

1. A cooling device for a fluid comprising at least two cold producing machines each having at least one compression space of variable volume which operates at a higher average temperature, at least two expansion spaces of variable volume co-acting with said compression space, said expansion spaces having successively lower average temperatures in order of succession, means communicating said spaces with each other and said means including at least one regenerator through which a working medium traverses, and a duct system through which said fluid to be cooled passes, said fluid to be cooled in said duct system being sequentially in thermal contact with said expansion spaces of gradually lower temperatures, said fluid in the duct system being first in thermal contact with said expansion space of the highest average temperature of one of said cold producing machines and thereafter with the corresponding expansion space of said other machine, said duct system being subsequently in thermal contact with each further group of corresponding expansion spaces of lower temperature.

2. A cooling device for a fluid as claimed in claim 1 further comprising a second duct system provided with a compressor, a pair of storage containers having a working medium therein, a pair of valves connected to one of said expansion spaces, one of said valves being opened at a predetermined time whereby said expansion spaces are filled with compressed working medium, and the other of said valves being opened at a predetermined time to permit the compressed working medium to be conducted into one of said storage containers and thereby cause a pressure drop in said cooling device.

References Cited UNITED STATES PATENTS 2,750,765 6/1956 Kohler et al. 626 2,820,352 1/1958 Fokker et al 6240 XR 3,101,597 8/1963 Dros 626 3,128,605 4/1964 Malaker et al.

3,221,509 12/1965 Garwin 626 3.310.954 3/1967 Systra et al 626 3,327,486 6/1967 Kohler et al. 626

NORMAN YUDKOFF, Primary Examiner.

V. W. PRETKA, Assistant Examiner. 

